This application relates to applications Ser. No. 870,789 and Ser. No. 870,788, filed on even date and of common assignee herewith.
1. Field of the Invention
This invention relates to fuel combustors and more specifically, to combustors for gas turbine engines in which fuel and air are mixed before injection into the combustion zone of the combustor.
2. Description of the Prior Art
Within the gas turbine engine field, combustion principles are among the most difficult phenomenon to describe and predict. Accordingly, over the last four decades, combustion apparatus has gone through dramatic alteration after alteration as new scientific theories and techniques are advanced.
Among the most recent and most promising techniques are those known generically with the industry as "swirl burning." Basic swirl burning concepts are discussed in U.S. Pat. No. 3,675,419 to Lewis entitled "Combustion Chamber Having Swirling Flow" and in U.S. Pat. No. 3,788,065 to Markowski entitled "Annular Combustion Chamber for Dissimilar Fluids in Swirling Flow Relationship." The concepts described in these patents are now employed to effect rapid and efficient combustion, yet stringent anti-pollution objectives are imposing further demand for advances in technology.
Perhaps the most imposing anti-pollution objective facing scientists and engineers is the requirement for reduced levels of nitrous oxide emission. Nitrous oxides are produced, for example, in accordance with the simplified reactions shown below. EQU N.sub.2 +O.sub.2 +Heat.fwdarw.2NO EQU 2NO+O.sub.2 .fwdarw.2NO.sub.2
The reactions require both the presence of oxygen and very high temperatures. Limiting either the oxygen present or the fuel combustion temperature substantially reduces the levels of nitrous oxide produced. Under normal conditions, the amount of oxygen in the combustor cannot be reduced without the deleterious side effect of increasing the level of hydrocarbon and carbon monoxide emissions. Excess oxygen is required to assure that the fuel is completely burned. It is, therefore, that reductions in combustor temperature and reductions in the time exposure of the free nitrogen and excess oxygen to the combustor temperature, offer more positive approaches to nitrous oxide reduction than limits on oxygen content.
One very recent advance for reducing the level of nitric oxide pollutants in combustor effluent is disclosed in U.S. Pat. No. 3,973,375 to Markowski entitled "Low Emission Combustion Chamber". In U.S. Pat. No. 3,973,375, combustor fuel is vaporized in the vitiated effluent of a pilot burner and is subsequently diluted to a lean fuel air ratio downstream thereof. Vaporizing the fuel in the vitiated effluent effects an ignition lag such that auto ignition does not occur before lean ratios are achieved.
Yet, further advances are desired and new techniques and concepts need be developed. To this end manufacturers and designers of gas turbine engines are continuing to direct substantial economic and personnel resources toward the advancement and attainment of anti-pollution objectives.